Dave,
While I've put my 1900 Swiss back in storage, I recall there being only two places with full serial numbers on the outside:
Full Serial Number:
�· Bottom of Barrel
�· Front of Frame
Last Two Digits:
�· Sideplate
�· Take Down Lever
�· Magazine Release
�· Rear Toggle Link
You may also find two digit numbers on the inside:
�· Trigger
�· Breech Block
�· Grips
Later Lugers may also have serial numbers on the firing pin and hold open catch.
Also, I've seen 1900 Swiss with all three saftey levers (I've included a picture, below). If yours is an early two digit Swiss, it should have a Type I safety.
